Cleaning formulations for specific use in machine dishwashers for cleaning soiled plates, glasses, cups, etc. have been disclosed in the prior art (see for example U.S. Pat. Nos. 3,579,455; 3,627,686; 3,673,098; 3,048,548 and 3,549,539). Generally, all of the conventional commercial dishwasher detergents are in the form of a powder and utilize non-ionic surfactants for the control of foam in the dishwasher.
In the course of early development work for the detergent compositions of the present invention, Applicants noted that a substantial amount of the powder detergent is lost from the dishwasher dispenser cup prior to utilization during the main wash cycle. Investigation revealed the cause to be leakage of the detergent from the closed dispenser cup which holds the detergent load for the second or main wash cycle. The dishwasher machines commonly available today operate by using one or two wash cycles followed by rinsing cycles. For those dishwashing machines having only one wash cycle, the dispenser cup remains closed until the beginning of that wash cycle when the detergent is released for cleaning purposes. For those machines having two wash cycles, the dispenser cup remains closed until the beginning of the second or main wash cycle when the detergent is released for cleaning purposes.
Further investigation revealed that all of the currently available commercial granular detergents, as well as powders, suffered from the same problem in varying degrees in different dishwashing machines, depending on the tightness of the dispenser door seal. The looser the fit of the door, the more the water could leak in and flush out the powder prior to utilization during the main wash cycle.
With this problem in mind, and also for the purpose of developing an improved low-foaming dishwasher detergent composition, Applicants carried on further investigative work and unexpectedly discovered that, by formulating the composition in the form of a gel characterized by having a minimum yield point value, the amount of detergent lost from the dispenser cup due to leakage is greatly minimized compared to that for powdered detergents.
Although several U.S. patents disclose liquid detergent formulations having thickeners therein for use in clothes laundry machines or automatic dishwashing machines, there does not appear to be any disclosure concerning this problem related to the leakage of the detergent from the dishwasher dispenser cup. For example, U.S. Pat. Nos. 3,060,124 and 3,075,922 are concerned with the use of thickeners to stabilize the liquid detergents from phase separation. However, these patents do not discuss the functional advantage of the gel form, characterized by having a minimum yield point, over the powders in retaining the detergent in the dispenser cup of an automatic dishwasher machine.